• 대한기계학회논문집A
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• 제40권7호
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• pp.653-658
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• 2016

가스터빈엔진의 고온 부품은 초내열 합금 재료를 이용하며, 냉각설계 적용으로 형상이 복잡하여 정밀 주조 과정을 거치게 된다. 터빈 부품에 주로 적용이 되는 일방향 응고 및 단결정 재료는 제조 과정에서 결정립 성장 방향이 설계와 다르게 섭동을 가지게 되며, 이는 각 방향에 대한 재료 상수의 섭동을 유발하여 응력 분포의 변화와 함께 피로 수명에 큰 산포를 야기하게 된다. 본 연구에서는 일방향 응고 재료 노즐에 대하여 결정립 성장 방향의 섭동에 대한 구조 건전성의 영향을 저주기 피로 수명을 통해 확인하여, 향후 제작 허용값에 대한 제안 및 좀 더 정교한 통계적 접근이 필요함을 확인하고자 한다. 이를 위해 복합 열전달 해석을 통해 금속 온도 분포를 계산하고 이를 근거로 구조 해석 및 저주기 피로 수명을 계산하였다.

• Tribology and Lubricants
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• 제36권5호
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• pp.253-261
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• 2020

In this paper, we present an experimental investigation of the frequency characteristics and a visual inspection of an oxidizer pump with a modified rear-floating ring seal for a 7-tonf turbopump. An oxidizer pump typically operates at high rotational speeds and under cryogenic conditions. Despite its low hydraulic efficiency, the floating ring seal is frequently employed as a leakage control solution for turbomachinery because it effectively reduces abrasion by friction. When the oxidizer pump starts up, the floating ring moves excursively but locks up stably against the pump casing when the contact pressure increases. The compressive force on the floating ring depends on the hydrodynamic forces induced by the flow through the floating ring. This force is controlled by the nose position of the floating ring. Based on a validation test for a 7-tonf turbopump with two types of floating rings, we concluded that the floating ring with a small diameter nose can move easily with a low contact pressure in the cooling path. This leads to instability of the pressure fluctuation around the floating ring. In contrast, a floating ring with a large diameter nose has a high contact pressure and attaches strongly to the casing, which causes wear and frictional oxidation between the contact surfaces of the impeller and the floating ring.

• International Journal of Korean Welding Society
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• 제3권2호
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• pp.40-45
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• 2003

A series of experiments has been carried out to investigate the effect of titanium, boron and nitrogen on the microstructure and toughness of simulated heat affected zone (HAZ) in quenched and tempered (QT) type 490MPa yield strength steels. For acquiring the same strength level, the carbon content and carbon equivalent could be lowered remarkably with a small titanium and boron addition due to the hardenability effect of boron during quenching process. Following the thermal cycle of large heat input, the coarsened grain HAZ (CGHAZ) of conventional quenched and tempered (QT) type 490MPa yield strength steels exhibited a coarse bainitic or ferrite side plate structure with large prior austenite grains. While, titanium and boron bearing QT type 490MPa yield strength steels were characterized by the microstructure in the CGHAZ, consisting mainly of the fine intragranular ferrite microstructure. Toughness of the simulated HAZ was mainly controlled by the proper Ceq level, and the ratio of Ti/N rather than titanium and nitrogen contents themselves. In the titanium­boron added QT steels, the optimum Ti/N ratio for excellent HAZ toughness was around 2.0, which was much lower than the known Ti/N stoichiometric ratio, 3.4. With reducing Ti/N ratio from the stoichiometric ratio, austenite grain size in the coarse grained HAZ became finer, indicating that the effective fine precipitates could be sufficiently obtained even with lower Ti/N level by adding boron simultaneously. Along with typical titanium carbo­nitrides, various forms of complex titanium­ and boron­based precipitates, like TiN­MnS­BN, were often observed in the simulated CGHAZ, which may act as stable nuclei for ferrite during cooling of weld thermal cycles

• The Korean Journal of Pain
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• 제10권2호
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• pp.220-224
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• 1997

Background: The incidence of pain on injection of propofol varies between 30 and 100%. A variety of pretreatments have been tried to alleviate this problem such as a local anesthetics, cooling and opioids. However, none of these pharmacological maneuvers were satisfactory yet. In a recent study, subhypnotic doses of both thiopental sodium and propofol decrease the acute pain. We report a comparison of thiopental sodium, lidocaine and placebo on the incidence and severity of pain on injection of propofol. Method: A controlled, double-blind study was performed to compare the prior administration of intravenous saline 2 ml(n=30, group S), lidocaine 20 mg(n=30, group L) and thiopental sodium 50 mg(n=30, group T) in alleviating the pain by propofol. Injection pain was assessed with the four-point verbal categorical scoring system. Result: The incidence of injection pain during induction was lower in group L(30%) and T(17%) than group S(77%). The incidence of injection pain was lower in group T(17%) than group L(30%), but not significant statistically. The pain scores for recall of pain in the recovery room was simlar to those pain during propofol induction. Conclusion: The pretreatment of thiopental sodium can be effective in reducing both incidence and severity of propofol injection pain and has similar effect to lidocaine to prevent propofol injection pain.

• Journal of Biosystems Engineering
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• 제27권5호
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• pp.433-450
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• 2002

The daily food intake for dairy cows has to be effectively controlled to breed a sound group of cows as well as to enhance the productivity of the cows. But, feed stuffs are fed in the common bulk for a group of cows in most cases despite that the individual food intake has to be varied. To obtain the feed for each cow, both the nutrient requirements and the nutrient composition of fred have to be provided in advance, which are based on the status of cows such as weigh marginal weight amount of milk, fat concentration in milk, growth and milking stages, and rough feed ratio, etc. Then, the mixed ration fur diet would be computed by the nutrient requirements constraints. However, when TMR (Total Mixed Ration) is conventionally supplied for a group of cows, it is almost impossible to get an optimal feed mixed ration meeting the nutrient requirements of each individual cow since the constraints are usually conflicting and over-constrained although they are linear. Hence, addressed in this paper is a simulated annealing (SA) technique to find the food intake for dairy cows, considering the characteristics of individual or grouped cows. Appropriate parameters fur the successful working of SA are determined through preliminary experiments. The parameters include initial temperature, epoch length. cooling scheduling, and stopping criteria. In addition, a neighborhood solution generation method for the effective improvement of solutions is presented. Experimental results show that the final solution for the mixture of feed fits the rough feed ratio and some other nutrient requirements such as rough fiber, acid detergent fiber, and neutral detergent fiber, with 100 percent, while fulfilling net energy for lactating, metabolic energy, total digestible nutrients, crude protein, and undegraded intake protein within average five percent.

• 한국세라믹학회지
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• 제55권4호
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• pp.344-351
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• 2018

The effects of bond coat species on the growth behavior of thermally grown oxide (TGO) layer in thermal barrier coatings (TBCs) was investigated through furnace cyclic test (FCT). Two types of feedstock powder with different particle sizes and distributions, AMDRY 962 and AMDRY 386-4, were used to prepare the bond coat, and were formed using air plasma spray (APS) process. The top coat was prepared by APS process using zirconia based powder containing 8 wt% yttria. The thicknesses of the top and bond coats were designed and controlled at 800 and $200{\mu}m$, respectively. Phase analysis was conducted for TBC specimens with and without heat treatment. FCTs were performed for TBC specimens at $1121^{\circ}C$ with a dwell time of 25 h, followed by natural air cooling for 1 h at room temperature. TBC specimens with and without heat treatment showed sound conditions for the AMDRY 962 bond coat and AMDRY 386-4 bond coat in FCTs, respectively. The growth behavior of TGO layer followed a parabolic mode as the time increased in FCTs, independent of bond coat species. The influences of bond coat species and heat treatment on the microstructural evolution, interfacial stability, and TGO growth behavior in TBCs are discussed.

• 한국항해항만학회지
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• 제33권5호
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• pp.303-308
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• 2009

최근 항공기, 자동차, 선박을 포함하여 다양한 분야에서 무인시스템에 관한 연구 개발이 이루어지고 있다. 우리나라에서도 IT 기술의 발달과 함께 무인시스템에 관한 연구가 활발히 진행되고 있지만 아직 개발 실적은 미미한 수준이다. 이 연구에서는 바지(barge)선형의 초소형자율 무인선박(USV)을 개발하고자 하였다. 자율항법 알고리즘 개발에 GPS센서의 위치 정보를 기반으로 대권항법 계산식을 적용하였으며, 프로그래밍은 NI사의 LabVIEW 8.2를 이용하였다. 조타제어는 펄스진폭변조 방식으로 하였다. 또한, 엔진시스템은 전동모터 및 전자 변속기로 구성하였고, 엔진시스템 냉각방식으로 DC모터펌프를 이용한 해수 직접냉각방식을 채용하였다. 무인선박을 자체 설계 제작하고, 해상실험을 통해 자율운항 알고리즘의 유효성을 검증하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.628-635
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• 2010

냉각기계를 적용한 환경조절계통의 성능은 항공기의 비행환경에 따라 엔진의 운전상태가 달라지므로 환경조절장치로 취출되는 공기의 상태(온도와 압력)에 따라 급격히 바뀌게 된다. 즉, 항공기의 운전상태에 따라 환경조절장치는 운용성능을 100%만족하는 영역에서 운전될 수도 있고, 그렇지 않을 수도 있다. 그렇기 때문에, 일반적으로 냉각기계를 적용한 환경조절장치의 설계규격은 항공기에서 요구하는 개발규격보다 큰 설계여유를 갖도록 설계한다. 이로 인한 시스템적인 손실요인을 최소화하기 위하여 본 연구에서는 냉각기계형 환경조절장치에 상변화 물질의 적용가능성을 연구하였다. 그 결과 상변화 현상을 이용하여 환경조절장치의 출구온도를 일정온도 범위 이내로 제어하면, 현재 운용되는 냉각기계형 환경조절장치의 일반적인 성능여유보다 적은 성능여유에서도 환경조절장치에 요구되는 성능요구조건을 만족할 수 있는 것으로 분석되었다. 본 연구 결과 환경조절장치의 운용개념 변경을 통하여 환경조절장치의 시스템 적용성 향상을 기대할 수 있을 것으로 판단된다.

• 설비공학논문집
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• 제17권10호
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• pp.914-921
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• 2005

In this study, the 1/20 reduced-scale experiment using Froude scaling were conducted to investigate the effect of longitudinal ventilation velocity on the burning rate in tunnel fires. The methanol pool fires with heat release rate ranging from 2.02 kW to 6.15 kW and the n-heptane pool fires with heat release rate ranging from 2.23 kW to 15.6 kW were used. The burning rate of fuel was obtained by measuring the fuel mass at the load cell. The temperature distributions were observed by K-type thermocouples in order to investigate smoke movement. The ventilation velocity in the tested tunnel was controlled by inverter of the wind tunnel. In methanol pool fire, the increase in ventilation velocity reduces the burning rate. On the contrary in n-heptane pool fire, the increase in ventilation velocity induces large burning rate. The reason for above conflicting phenomena lies on the difference of burning rate. In methanol pool fire, the cooling effect outweighs the supply effect of oxygen to fire plume, and in n-heptane pool vice versa.

• KIEAE Journal
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• 제16권4호
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• pp.63-69
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• 2016

Purpose: This preliminary study investigated a potential of the water wall systems that provide heat storage and natural lighting control simultaneously. Method: In order for transparency of the water wall to be controlled, the study first proposed two measures: to adjust transparency of the water wall; to control transparency of water wall surface. The performance of two measures then was verified and compared by experiments. In addition, a trade-off between heat collect and heat storage resulting from using additive for adjusting transparency was investigated. Result: The experiment showed that the two measures are similar in performance. The investigation of trade-off relation showed the additive should have the same heat storage as the water to prevent decrease in thermal performance of the water wall. As an economical measure to control transparency of the water wall, this study suggested a measure of secondary heat transfer systems using shading device that first absorbs solar radiation and then transfers heat to the water wall. The experiment show that performance of the proposed measure is similar to controlling transparency of water wall surface. In conclusion, it is expected that the performance of the water wall can be economically maximized by using the proposed mean in terms of heating, cooling and lighting energy saving.